Many tools are available for making multiplex measurements on biological cells in aggregate, but few tools exist to measure the chemistries and compositions within individual cells, particularly live cells and at multiple time points. The methods that do exist are largely based on microscopy and use absorbance or fluorescence of small numbers of markers within cells, and are not capable of making multiplex measurements within complex samples extracted from multiple cells. Measurement of live cells typically involves the immersion of the cells in a liquid medium to maintain the vitality of the cells and keep them in a biologically relevant state for long periods of time. Conditions that are out of the ordinary expose the cells to damage and stresses that confound many biological measurements.
Small-scale capillaries and pipettes have been utilized to inject proteins, peptides, and genetic materials into living cells. However, these techniques are prone to damaging the cells. Moreover, the positioning of capillaries and pipettes is often difficult to accurately control even with the assistance of optical microscopy. Atomic force microscopy (AFM) probe tips, conventionally employed for high-resolution imaging of cell surfaces or force spectroscopy measurements, are being investigated for use as cell probes because AFM force/position feedback signals may be utilized for accurate positioning of the probe and determining when the probe has contacted, indented, and penetrated the cell membrane. For example, an AFM probe tip or a needle formed from an AFM probe tip has been utilized to extract cell components from cells by inserting the AFM probe tip into the cell. Cell components may be retained on the AFM probe tip by physical adsorption to the probe surface or binding to receptors on the probe surface. An AFM probe tip has also been modified to provide a single microfluidic channel capable of dispensing a liquid into a cell. Thus far, however, none of the known probes employed to penetrate cells have been capable of independently injecting material into and extracting fluid from cells utilizing microfluidic channels, or extracting multiple samples from the same cell or multiple cells in a manner in which each sample is isolated from the other samples.
Therefore, there is a need for devices and methods that perform operations on cells while minimizing damage, stress, and unwanted alteration of the cells. There is also a need for devices and methods that enable the independent injection of material into, and extraction of material from, individual cells, as well as other types of single-cell manipulations. There is also a need for devices and methods that enable extraction of multiple samples from cells while keeping each sample isolated from the other samples.